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/*
 * de.unkrig.commons - A general-purpose Java class library
 *
 * Copyright (c) 2020, Arno Unkrig
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification, are permitted provided that the
 * following conditions are met:
 *
 *    1. Redistributions of source code must retain the above copyright notice, this list of conditions and the
 *       following disclaimer.
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 *       following disclaimer in the documentation and/or other materials provided with the distribution.
 *    3. Neither the name of the copyright holder nor the names of its contributors may be used to endorse or promote
 *       products derived from this software without specific prior written permission.
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 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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package de.unkrig.commons.lang.protocol;

/**
 * Various {@link Relation}-related utility methods.
 * 
 *   Examples:
 * 
 * {@code
 *   Relation greaterOrEqual = Relations.not(Relations.lessThan());
 * }
 */
public final
class Relations {

    private
    Relations() {}

    /**
     * @return A {@link Predicate} that relates the subject to the rhs
     */
    public static > Predicate
    compareWithConstant(final Relation relation, final T rhs) {

        return new Predicate() {
            @Override public boolean evaluate(T subject) { return relation.evaluate(subject, rhs); }
            @Override public String  toString()          { return relation.toString() + " " + rhs; }
        };
    }

    /**
     * @return A {@link Relation} that evaluates {@code true} iff the lhs is greater than the rhs
     */
    @SuppressWarnings("unchecked") public static > Relation
    greaterThan() { return (Relation) Relations.GREATER_THAN; }

    /**
     * @return A {@link Relation} that evaluates {@code true} iff the lhs is less than the rhs
     */
    @SuppressWarnings("unchecked") public static > Relation
    lessThan() { return (Relation) Relations.LESS_THAN; }

    /**
     * @return A {@link Relation} that evaluates {@code true} iff the lhs is equal to the rhs
     */
    @SuppressWarnings("unchecked") public static > Relation
    equalTo() { return (Relation) Relations.EQUAL_TO; }

    /**
     * @return A {@link Relation} that evaluates to the negation of the delegate relation
     */
    public static > Relation
    not(final Relation delegate) {
        return new Relation() {

            @Override public boolean
            evaluate(Comparable lhs, Comparable rhs) { return !delegate.evaluate(lhs, rhs); }

            @Override public String
            toString() { return "!" + delegate.toString(); }
        };
    }

    @SuppressWarnings({ "rawtypes", "unchecked" }) private static final Relation
    GREATER_THAN = new Relation() {
        @Override public boolean evaluate(Comparable lhs, Comparable rhs) { return lhs.compareTo(rhs) > 0; }
        @Override public String  toString()                               { return ">"; }
    };
    @SuppressWarnings({ "rawtypes", "unchecked" }) private static final Relation
    LESS_THAN = new Relation() {
        @Override public boolean evaluate(Comparable lhs, Comparable rhs) { return lhs.compareTo(rhs) < 0; }
        @Override public String  toString()                               { return "<"; }
    };
    @SuppressWarnings({ "rawtypes", "unchecked" }) private static final Relation
    EQUAL_TO = new Relation() {
        @Override public boolean evaluate(Comparable lhs, Comparable rhs) { return lhs.compareTo(rhs) == 0; }
        @Override public String  toString()                               { return "=="; }
    };
}